There are many known types of flowmeters for metering water: wet flowmeters in which both the mechanism and the indicator rolls are completely immersed in the liquid, and dry or extra dry flowmeters in which the indicator rolls are situated in a leak-proof chamber. The present invention relates only to water meters of the dry or extra dry type.
The indicator rolls of such flowmeters are read through a transparent window. If the dry chamber is not perfectly leak-proof, condensation can form on the inside surface of the window which makes reading the indications on the rolls difficult or impossible.
A device is known which is used to remove the condensation from the inside surface of the window of a dry or extra dry flowmeter. Such a device is shown in FIGS. 1 and 2.
FIG. 1 shows a schematic view from above of a prior art flowmeter, and FIG. 2 shows a section through the flowmeter on line AA. The device for wiping the window comprises a control knob 10 which is operable from outside the flowmeter and which passes sealingly through the window of the flowmeter. A spindle 14 extending from the knob 10 supports a blade 16 which is perpendicular to the spindle.
The upper surface of the blade 16 includes a longitudinal slot 18. A felt or rubber part 20 is secured in the slot 18 so as to rub against the inside surface 22 of the flowmeter window.
If reading of the rolls 24 which indicate the measurement of the flowmeter is prevented by condensation formed on the inside surface 22 of the window, the user operates control knob 10. As the blade is set in rotation, the rubbing action of the felt part 20 removes the condensation from the inside surface 22 of the window above the rolls 24.
This type of window wiper has disadvantages. As far as manufacture of the device is concerned, the felt part 20 has to be incorporated in the space 18 provided for it. This is a delicate operation which complicates the manufacturing process.
Moreover, the blade and the felt or rubber part are not transparent; consequently, that assembly masks the rolls of the flowmeter and hinders reading.